Terrestrial deposits on intertidal sandflats: sediment characteristics as indicators of habitat suitability for recolonising macrofauna

Elevated rates of sedimentation as a result of human activities is a recognised problem in many marine environments. Thus, it is important to develop a mechanistic understanding of the impact and subsequent recovery of terrestrial sediment deposits in these areas. This paper describes an experiment to investigate possible reasons for the slow recovery of intertidal soft-sediment macrofaunal communities following smothering by storm-associated terrestrial sediment deposits. We measured, and monitored changes in, a large number of physical and biogeochemical properties of terrestrially derived sediments, in order to identify those characteristics that were most important to potential colonists. Properties of the terrestrial sediments were remarkably different to those of the surrounding sandflat and showed little signs of change over the duration (4.5 mo) of the experiment. Despite this, we were able to identify that temporal changes in macrofaunal community composition were strongly correlated with the levels of chl a, total carbohydrate, phosphorus (P), nitrogen (N) and coarse sand in the sediments, We recommend that future studies of macrofaunal recolonisation following deposition of terrestrial sediment should include measurement of these sediment properties. In addition, analyses which isolate the biologically available portions of carbohydrate, P and N may provide even more insight as to the importance of these properties as settlement cues and indicators of recovery. We also assessed the influence on macrofaunal communities of the conditioning the sediment receives prior to being deposited on the sandflat (i.e. mixing with seawater or freshwater), and found no effect of this on the impact on existing macrofaunal communities or on the subsequent recovery of sediments or macrofauna.